I got the attached presentation sent by Heinz-Peter Mang and thought it could be useful for people working with biogas digesters and reuse of digestate in agriculture. It is not so easy to geld hold of such information from China.

The ppt is about the application of the digestate as fertiliser.

It is a short version of USTB/CSES training ppts which were used in a IDCOL-NDBMP training seminar on digestate utilisation in Bangladesh in 2012 (with support by KfW).
Before anyone asks: I also don't know what IDCOL-NDBMP is...
But USTB/CSES is epxlained in the ppt: Centre of Sustainable Environmental Sanitation
University of Science and Technology Beijing , P.R.China

I have two questions for Heinz-Peter:

(1)
The presentation talks about digested effluent and shows a slide (number 12) where people are spraying something that looks like water but the slide says "anaerobic digestate". I thought what comes out of such a digester is a slurry that is difficult to settle - so how can it be sprayed through such nozzles?

(2)
Secondly, the presentation mentions on slide 8:

Hygienic standard for the anaerobic digestate fertilizer should meet the requirements of Table 2 of GB 7959-1987, see Annex B.

What are the required hygienic standards? From my understanding, biogas digesters are not particularly strong on destroying pathogens. The helminth eggs may settle well but wouldn't you still find them in the slurry? By which mechanism would they get killed in a digester?

Regards,
Elisabeth

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b) Anaerobic digestate consists of (i) BIOL = Bioliquid and (ii) BIOSOL = biosolids (see chapter on the GTZ biogas film from 1992, it has been scientifically developed in Peru, then first applied in Bolivia, China, Nigeria), separation occurs by post-composting (leachate of the compost pile = BIOL), by sedimentation or filtration or drainage beds (subject to the requirements of further reuse application). BIOL will normally be further diluted with water for foliar fertilization, seed treatment, and used as biopesticides in the corn and fruit or flowers in the production. BIOSOL is used mostly for soil improvement or for fungal cultures.

c) The Chinese standard GB7959 requires that for the (co-) treatment of human faeces in biogas plants, a post-composting (which is usually the standard applied) or thermophilic fermentation is used. A non-authorised translation of the Chinese standard GB into English is attached below.

I know it seems a bit odd to watch a biogas movie from 1991 but the funny thing about biogas technology for human and animal excreta is that it was peaking in the 1990s and the publications from then are still pretty valid (I am told)!

Regards,
Elisabeth

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And I had one more question about pathogen kill in anearobic digesters:
I had asked (above):

From my understanding, biogas digesters are not particularly strong on destroying pathogens. The helminth eggs may settle well but wouldn't you still find them in the slurry? By which mechanism would they get killed in a digester?

Answer by Heinz-Peter Mang (thank you!!):
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The question with the helmith egg was answered already in the GIZ-ecosan-Technology review "Biogas sanitation" (www.susana.org/lang-en/library?view=ccbk...mp;type=2&id=877). "Helminth" means parasitic worm, including : Ascaris lumbricoides (sometimes called just "Ascaris"), and hookworm (Anclostoma duodenale and Necator americanus). In the table "Effects of anaerobic sanitization on selected pathogens and parasitic ova as well as on E-Coli indicator (source: Zhang Wudi, BRTC, China 1985)" it is explained that these ovas (eggs) have 98.8 to 100% fatality after 10-36 days in mesophilic conditions and 53-90% fatality after 30-100 days in ambient temperature fermentation.

As we have in conventional simple biogas sanitation systems a separation of a long sludge retention time through sedimentation and scum formation vs. a short liquid retention time, settled ovas are treated. This differentiation of the hydraulic rentention time does not happen in Completely Stirred Tank Reactors (CSTR). And as explained in the Technology review: "Chinese, and Dutch as well as German studies showed that there is a complete inactivation of the pathogenic test organisms through aerobic post composting process." See also some confirming new research work from Nigeria (attached) and from SANSED.
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Most basic digesters that I know of in developing countries operate at ambient temperatures or at the most mesophilic (35 °C). This means we get some helminth egg kill (according to the above 53-90%) but not total. It would in fact be better to quote the log reduction, I guess. That's fine by me, it means that the WHO multi-barrier approach still needs to be applied.

Elisabeth

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May I add some "old" stuff from the 1970s: Jean Pain - The power of compost

Jean Pain (1930 - 1981) was a French innovator who developed a compost based bioenergy system that produced 100% of his energy needs. He heated water to 60 degrees Celsius at a rate of 4 litres a minute which he used for washing and heating. He also distilled enough methane to run an electricity generator, cooking elements, and power his truck. This method of creating usable energy from composting materials has come to be known as Jean Pain Composting, or the Jean Pain Method.

Maybe it is a good idea to have for "old" but still very relevant stuff a separate section open?

This is an interesting discussion on the use of anaerobic digestate. I would be very cautious in using it.

Excreta and wastewater generally contain high levels of excreted pathogens, especially in regions where intestinal parasites and diarrhoeal diseases are prevalent. Many infections are controlled or favoured by the use of wastewater, or, as in the present case, the anaerobic digestate.

All excreted pathogens and helminths can survive for a period of time, long enough to pose health risks to the workers. Helminth eggs and amoebic cysts settle to the bottom of the digesters, where they remain viable for long periods of time, mesophilic range of temperature notwithstanding.

According to Feachem et al. (1983), survival times of Helminths (Ascaris lumbricoides eggs, Hookworm larvae, Taenia saginata eggs, and Trichuris trichuiura eggs) are many months. Strauss (1985) has also reviewed the survival times of pathogens.

As an monitoring and evaluation activity, I would be interested if Heinz-Peter Mang kindly provide prevalence of the pathogen-related diseases, before and after the application of the digestate, in the areas where it is applied in China.

For Ms. Elisabeth:

If possible and permissible (copyright laws), please get the following excellent publications and put them in the SuSanA library:

After I made those posts above on Heinz-Peter's behalf, I had a couple more e-mails with him. I copy them here because they might answer some of your questions to some extent:

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From Heinz-Peter Mang on 9 April:

Anaerobic digestion will eliminate >99% of most pathogens - why? METHANOGENIC BACTERIAS CALLED OBLIGATE ANAEROBES WHICH CANNOT LIVE IN THE PRESENCE OF FREE OXYGEN. Methanogens use CO2 to oxidize H2, and release methane as a waste product. During fermentation the methanogen archaea bacteria became the dominant inhabitants and as they have a larger surface-to-volume ratio than E. coli and most pathogens, Archaea bacteria can out-compete E. coli and most pathogens for nutrients and substrates. Therefore, reduction in numbers of E. coli and some pathogens occurs! Archaea bacteria are adsorbed (flocculated) to floc particles or biofilm and remain for long sludge retention time (SRT) in the treatment process. Flocculation reduces the number of dispersed bacterial cells including E. coli and pathogens and eggs that are present in the secondary effluent!

Side effect of anaerobic wastewater treatment: Because methanogene archaea bacterias are able to reduce significantly the quantity of C-BOD and N-BOD (ammonia) in the effluent, the chlorine demand for disinfection of E. coli and pathogens is reduced.

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Second e-mail from Heinz-Peter Mang on 9 April:

Helminths form three main life-cycle stages: eggs, larvae and adults. Eggs pass through the intestinal tract and are eliminated from the body in the feces. Within two days, the eggs hatch in warm, moist soil. The larvae live in the soil, waiting for contact with a host. The first form of the larval stage is called rhabditiform larva and exists in contaminated feces or soil. For five to 10 days, the larva will grow and molt twice. After the last molt, larvae will enter a filariform stage and can then infect a host. Filariform larvae can survive for up to a 30 days in the soil.

Lack of oxygen in the biogas process will inhibit the development of these preparasitic stageslarvae and adults. Sedimentation is most effective as helminths eggs do not float well in solutions. The higher the specific gravity of the biogas feedstock mixture, the more helminths eggs of various types will be recovered also in the floating scum layer of simple not-mixed biogas plants. One of the most critical parameter to determine the die-off process is also the amount of ammonia in the feedstock which as longer retention periods are needed for parasite egg die-off if the ammonia content is too low. But the sludge produced contains even after 100 days sludge retention time still some pathogens (notably some helminth eggs) and requires further treatment (composting, aeration) before any application to agricultural land.

The other two publications that you mentioned are so old that the challenge is to get them in digital format - pdf file? A scanned version? If someone can provide a digital version, then they can be added to the SuSanA library. (Google Books?)